Thioethers as Dichotomous Electrophiles for Site-Selective Silylation via C−S Bond Cleavage

The development of aryl alkyl sulfides as dichotomous electrophiles for site-selective silylation via C−S bond cleavage has been achieved. Iron-catalyzed selective cleavage of C(aryl)−S bonds can occur in the presence of β-diketimine ligands, and the cleavage of C(alkyl)−S bonds can be achieved by t-BuONa without the use of transition metals, resulting in the corresponding silylated products in moderate to excellent yields. Mechanistic studies suggest that Fe−Si species may undergo metathesis reactions during the cleavage of C(aryl)−S bonds, while silyl radicals are involved during the cleavage of C(alkyl)−S bonds.     

Simultaneous measurement of temperature and strain using a long-period fiber grating with a micro-taper

An all-fiber Mach–Zehnder interferometer (MZI) consisting of a long-period fiber grating with a micro-taper is proposed for simultaneous measurement of temperature and strain. The experimental results demonstrate that the temperature and strain sensitivities of the proposed MZI are 83 pm/°C and ?2.6 pm/με, respectively. The strain sensitivity is 20 times as high as that of a long-period fiber written by CO₂ laser pulses combined with a fiber bitaper. In addition, the interferometer requires only a common single-mode fiber, and it is easy to fabricate and is inexpensive for temperature and strain sensing applications.     

Distributional expansion of maximum from logarithmic general error distribution

Logarithmic general error distribution is an extension of lognormal distribution. In this paper, with optimal norming constants the higher-order expansion of distribution of partial maximum of logarithmic general error distribution is derived.     

基于辅因子化学本质及功能的分类与讨论

辅因子是蛋白质或酶结构的重要组成部分,在许多酶的功能中发挥重要乃至关键作用。在科研和教学中,现有的辅因子概念及其分类系统不够清晰准确。本文从化学本质和功能上将辅因子分为催化型、载体型和底物型3类,并以若干典型的辅因子为例讨论辅因子的特异性及再生性等问题。     

Rapid screening,identification, and purification of neuraminidase inhibitors from Lithospermum erythrorhizon Sieb.et Zucc. by ultrafiltration with HPLC–ESI‐TOF‐MS combined with semipreparative HPLC

We put forward an efficient strategy based on bioassay guidance for the rapid screening, identification, and purification of the neuraminidase inhibitors from traditional Chinese medicines, and apply to the discovery of anti‐influenza components from Lithospermiun erythrorhizon Sieb.et Zucc. Ultrafiltration with high‐performance liquid chromatography and electrospray ionization time‐of‐flight mass spectrometry was employed for the rapid screening and preliminarily identification of anti‐influenza components from Zicao. Semipreparative high‐performance liquid chromatography was used for the rapid separation and purification of the target compounds. NMR spectroscopy, mass spectrometry, and UV spectroscopy were used for further structural identification, and the activity of the compounds was verified by in vitro assay. Five compounds were found to have neuraminidase inhibitory activity by this method. Subsequently, the five compounds were separated by semipreparative high‐performance liquid chromatography with the purity over 98% for all of them by high‐performance liquid chromatography test. Combined with the NMR spectroscopy, mass spectrometry, and UV spectroscopy data, they were identified as alkannin, acetylalkannin, isobutyrylalkannin, β,β‐dimethylacryloylalkannin and isovalerylalkannin. The in vitro assay showed that all five compounds had good neuraminidase inhibitory activities. These results suggested that the method is highly efficient, and it can provide platform and methodology supports for the rapid discovery of anti‐influenza active ingredients from complex Chinese herbal medicines.     

Synthesis of aromatic liquid crystals with asymmetric diester based on rod-like multi-ring system by two-step esterification method

A novel method of two-step esterifications was developed to synthesize compounds with asymmetric double ester groups. By using this method, six rod-like double ester compounds were prepared with p-hydroxy benzaldehyde, p-hydroxy benzoic acid bicyclohexyl carboxylic acid, cyclohexyl benzoic acid and biphenyl carboxylic acid substituted by n-propyl and n-pentyl as main reactants. The structures and properties of target compounds were confirmed by IR, MS, ¹H NMR, elemental analysis, differential scanning calorimetry (DSC) and hot stage polarizing optical microscope (HS-POM). Typical yields of the target molecules were more than 70%. All the molecules have mesophases with the textures of nematic type, indicating a rod-like molecule with a longer rigid skeleton can keep its mesophases. There was no clearing point observed for any of the derivatives before they decomposed so that the temperature ranges of the mesophases could not be determined. The energy differences between frontier molecular orbitals (HOMO-LUMO) (E_g) of the compounds were calculated by cyclic voltammetry (CV). The terminal ring system has an obvious influence on the energy levels and the energy gaps (E_g).     

Synthesis and characterization of monodisperse oligo(fluorene-co-bithiophene)s

A series of monodisperse oligo(9,9-di-n-octylfluorene-co-bithiophene)s (OFbTs) with molecular lengths of up to 19.5 nm and molecular weights up to 7025 g mol(-1) has been synthesized by a divergent/convergent approach involving Stille coupling reactions. Stille coupling is quite efficient in preparing this class of oligomers, and even the molecule with nine fluorene units and eight bithiophene units (F9Th16) can be synthesized in a yield as high as 70 %. Because of easy functionalization of the thiophene ring at its alpha position, no additional protecting group allowing activation for further reaction is necessary. However, the synthetic routes must be optimized to eliminate contamination of the targeting compounds with the homocoupling product of the organotin reagents. Synthesis of the longest oligomer F13Th24 in a relative large quantity is limited by its low yield due to the pronounced ligand-exchange side reactions of the starting materials and reaction intermediates. All oligomers longer than F4Th6 are nematic mesomorphs and exhibit enhanced glass transition temperature and clearing point with increasing molecular length, as revealed by differential scanning calorimetry and polarizing optical microscopy. Absorption and photoluminescence (PL) measurements reveal that OFbTs are well-conjugated systems with an effective conjugation length longer than the length of F13Th24.     

Syntheses, structures, magnetism, and optical properties of lutetium-based interlanthanide selenides

Ln3LuSe6 (Ln = La, Ce), beta-LnLuSe3 (Ln = Pr, Nd), and LnxLu4-xSe6 (Ln = Sm, Gd; x = 1.82, 1.87) have been synthesized using a Sb2Se3 flux at 1000 degrees C. Ln3LuSe6 (Ln = La, Ce) adopts the U3ScS6-type three-dimensional structure, which is constructed from two-dimensional 2(infinity)[Ln3Se6](3-) slabs with the gaps between these slabs being filled by octahedrally coordinated Lu(3+) ions. The series of beta-LnLuSe3 (Ln = Pr, Nd) are isotypic with UFeS3. Their structures include layers formed from LuSe6 octahedra that are separated by eight-coordinate Ln(3+) (Ln = Pr, Nd) ions in bicapped trigonal prismatic environments. Sm1.82Lu2.18Se6 and Gd1.87Lu2.13Se6 crystallize in the disordered F-Ln2S3 type structure with the eight-coordinate bicapped trigonal prismatic Ln(1) ions residing in the one-dimensional channels formed by three different double chains via edge- and corner-sharing. These double chains are constructed from Ln(2)Se7 monocapped trigonal prisms, Ln(3)Se6 octahedra, and Ln(4)S6 octahedra, respectively. The magnetic susceptibilities of beta-PrLuSe3 and beta-NdLuSe3 follow the Curie-Weiss law. Sm1.82Lu2.18Se6 shows van Vleck paramagnetism. Magnetic susceptibility measurements show that Gd1.87Lu2.13Se6 undergoes an antiferromagnetic transition around 4 K. Ce3LuSe6 exhibits soft ferromagnetism below 5 K. The optical band gaps for La3LuSe6, Ce3LuSe6, beta-PrLuSe3, beta-NdLuSe3, Sm1.82Lu2.18Se6, and Gd1.87Lu2.13Se6 are 1.26, 1.10, 1.56, 1.61, 1.51, and 1.56 eV, respectively.     

Density functional theory study of the platinum-catalyzed cyclopropanation reaction with olefin

A computational study of the platinum-catalyzed cyclopropanation reaction with olefin is presented. The model system is formed by an ethylene molecule and the active catalytic species, which forms from a CH2 fragment and the Cl2Pt(PH3)2 complex. The results show that the active catalytic species is not a metal-carbene of the type (PH3)2Cl2Pt=CH2 but two carbenoid complexes which can exist in almost two degenerate forms, namely (PH3)2Pt(CH2Cl)Cl (carbenoid A) and (PH3)Pt(CH2PH3)Cl2 (carbenoid B). The reaction proceeds through three pathways: methylene transfer, carbometalation for carbenoid A, and the reaction of a monophosphinic species for carbenoids (A and B). The most favored reaction channel is methylene transfer pathway for (PH3)Pt(CH2PH3)Cl2 (carbenoid B) species with a barrier of 31.32 kcal/mol in gas phase. The effects of dichloromethane, THF, and benzene solvent are investigated with PCM method. For carbenoid A, both methylene transfer and carbometalation pathway barriers to reaction become remarkably lower with the increasing polarity of solvent (from 43.25 and 52.50 kcal/mol for no solvent to 25.36 and 38.53 kcal/mol in the presence of the dichloromethane). In contrast, the reaction barriers for carbenoid B via the methylene transfer path hoist 6.30 kcal/mol, whereas the barriers do not change significantly for the reaction path of a monophosphinic species for carbenoids (A and B).     

Unlocking the Remarkable Influence of Intramolecular Group Rotation for Third-order Nonlinear Optical Properties

This work exposes for the first time the remarkable influence of intramolecular group rotation on third-order nonlinear optical (NLO) performance. In order to prove the role of group rotation, we designed and synthesized two photo-response compounds tetramethyl 5,5′-(((diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis(methylene))diisophthalate (1) and 5,5′-(((diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis(methylene))diisophthalic acid (2) and investigated their NLO performance under different substituent (benzyloxy group) rotation states. 1 and 2 have dynamic benzyloxy group rotation in dilute solution and shows reverse saturated absorption (RSA). When the benzyloxy group rotation of 1 and 2 was restricted by PMMA, their NLO performance not only converted into saturated absorption (SA) and NLO refraction behaviours, but also hardly changed after isomerization. Interestingly, we also restricted the benzyloxy group rotation in solution to a certain extent through photo-induced trans→cis isomerization, and found that the NLO performances of cis isomers of 1 and 2 exhibit SA and positive refraction and are similar to those of 1 -PMMA and 2 -PMMA. This work provides a new exploratory method for studying the influencing factors of third-order NLO performance.